The present invention relates to an ink-jet head for ejecting ink drops to paper or the like to perform printing, a method of manufacturing the same, and an ink-jet recording apparatus on which the ink-jet head is mounted.
Recently, a very small actuator has been demanded for use in an ink-jet recording apparatus for the purpose of high-speed and high-precision printing with the development of a multi-nozzle structure and for the purpose of miniaturization of the apparatus. To this end, there is an ink-jet recording apparatus using static electricity for an actuator (for example, JP-A-6-71882). The ink-jet head is characterized in that an electrostatic actuator is formed of parallel plate electrodes, so that the actuator can be miniaturized and a multi-nozzle structure can be realized.
FIGS. 10 and 11 are a sectional view and a plan view, respectively, of a conventional ink-jet head driven by an electrostatic actuator. The ink-jet head shown in FIG. 10 and FIG. 11 has a lamination structure in which an electrode glass substrate 100, a diaphragm substrate 200, and a nozzle plate 300 are laid on the top of one another and bonded with each other. An ink supply port 104 is formed in the electrode glass substrate 100, and ink 400 is supplied from the ink supply port 104 to a reservoir 204 formed in the diaphragm substrate 200. The ink 400 is equally distributed to a plurality of cavities 203 through orifices 302 defined by the nozzle plate 300 and recess portions of the diaphragm substrate 200. The lower surface of each of the cavities 203 is constituted by a transformable diaphragm 201. This diaphragm 201 faces an individual electrode 101 through an air gap and an insulating film 200 for preventing short-circuit so as to constitute an electrostatic actuator. A common electrode 205 is disposed on the diaphragm substrate 200. An voltage is applied between the diaphragm 201 and the individual electrode 101 through this common electrode 205, so that an electrostatic attractive force is generated to transform the diaphragm 201 downward. After that, an ink drop 401 is ejected from a nozzle 301 by the pressure due to the spring force of the diaphragm 201 which is generated when the applied voltage is removed.
In the above-mentioned electrostatically driven ink-jet head, it is regarded as being preferable, from the point of practical view, to drive the electrostatic actuator by a driving voltage of 100 V or less. In order to drive the electrostatic actuator by a driving voltage of 100 V or less, the distance between the insulating film 202 of the electrostatic actuator and the individual electrode 101 is formed accurately to be in a range of from 2,000 to 3,000 angstroms. To this end, a diaphragm substrate constituted by a silicon single-crystal substrate having a bonded surface mirror-finished with high precision was required to be bonded, by anode-bonding, directly with an electrode glass substrate constituted by a borosilicate glass substrate and provided with a step by etching. In this case, however, there is a problem that such a silicon substrate mirror-finished with high precision is expensive and hard to obtain. In addition, in order to obtain required strength, it is necessary to use a thin silicon single-crystal substrate and reduce the height of partitions between respective cavities because the thickness of the partitions are reduced in accordance with the high density of nozzles. However, it is extremely difficult to handle such a thin silicon single-crystal substrate, and particularly there is another problem that it is difficult to increase the size of the substrate.
By the way, there is a method in which etching of a sacrificial layer is used to produce such a narrow gap as described above. For example, a method in which a sacrificial layer is formed and then the sacrificial layer is removed by etching so as to form air gaps is proposed in JP-A-10-510374, page 8 and U.S. Pat. No. 5,459,610 in FIG. 2. However, all the air gaps are provided for electrostatically modulating positions of the reflecting surface of a light valve. In addition, all the air gaps are made open, unlike closed air gaps formed between insulating film and individual electrodes of an electrostatic actuator of an ink-jet head. It is therefore impossible to apply the technique disclosed in the above-mentioned publications or the like as it is to the manufacturing of an ink-jet head.
It is an object of the present invention to provide an ink-jet head and a manufacturing method thereof, in which a substrate low in cost, easy to handle and large in size can be used to improve the productivity.
It is another object of the present invention to provide an ink-jet recording apparatus mounted with an ink-jet head manufactured by the above-mentioned manufacturing method.
(1) One aspect of the present invention is an ink jet head comprising a plurality of nozzle holes, ejection chambers independent of each other and communicating with the nozzle holes respectively, electrically conductive diaphragms constituting parts of the respective ejection chambers, and individual electrodes facing the diaphragms through air gaps respectively, and ejecting ink in the ejection chambers toward recording paper through the respective nozzle holes by applying voltages between the diaphragms and the individual electrodes to thereby transform the diaphragms, wherein the air gaps are formed by sacrificial layer etching. In the present invention, since the air gaps are formed by sacrificial layer etching, the air gaps can be formed with high precision, for example, in a range of from 2,000 to 3,000 angstroms, so that it is possible to drive the ink-jet head by a driving voltage of 100 V or less. In addition, it is not necessary to use a silicon single-crystal substrate, so that the substrate can be made layer in size. Therefore, the inkjet head can be suitably adapted for a line printer or the like having a multi-nozzle.
(2) Another aspect of the present invention is a method of manufacturing an ink-jet head comprising a plurality of nozzle holes, ejection chambers independent of each other and communicating with the nozzle holes respectively, electrically conductive diaphragms constituting parts of the respective ejection chambers, and individual electrodes facing the diaphragms through air gaps respectively, and ejecting ink in the ejection chambers toward recording paper through the respective nozzle holes by applying voltages between the diaphragms and the individual electrodes to thereby transform the diaphragms, wherein the air gaps are formed by sacrificial layer etching. In the present invention, since a sacrificial layer can be formed in a thin film process such as vapor deposition, CVD, or the like, a silicon single-crystal substrate mirror-finished with high precision is not required and electrostatic actuators can be formed only in such a thin film process. It is therefore possible to use a large-sized glass substrate, and thereby improve the productivity.
(3) A further aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (2), wherein the individual electrodes are formed on a substrate; an insulating film, a sacrificial layer and a diaphragm layer are subsequently formed so as to cover the individual electrodes; and window portions are formed in the diaphragm layer in part of predetermined positions where support portions of the diaphragms are to be located to perform the sacrificial layer etching through the window portions. Since the window portions are formed at places corresponding to the support portions of the diaphragms in such a manner and no aperture portion is formed in the diaphragms themselves, there is no deterioration in the properties of the diaphragms. In addition, it will go well if etching liquid permeates the sacrificial layer in its short-side direction through the window portions. Therefore, there is an advantage that it is easy for the etching liquid to permeate the sacrificial layer. The insulating layer, the sacrificial layer and the diaphragm layer may be formed in the order of the insulating layer, the sacrificial layer and the diaphragm layer, or in the order of the sacrificial layer, the insulating layer and the diaphragm layer.
(4) A still further aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (3), wherein slit portions are formed in the sacrificial layer and the diaphragm layer in positions where the window portions in the predetermined positions are not formed. Since the support portions are formed in the slit portions as they are, the support portions become so firm that the diaphragms can be supported stably.
(5) Another aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (3), wherein a plurality of window portions are dispersively formed for each of the air gaps. Since the window portions are dispersively formed, the sacrificial layer etching is performed uniformly. In addition, although the portions where the window portions are located are weak and apt to lift in the manufacturing process, the strength is increased by dispersively forming the window portions, so that the ink-jet head can be manufactured easily.
(6) A further aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (2), wherein the window portions are closed to form cavity partitions after the sacrificial layer etching. As a result, it is possible to obtain a closed structure efficiently, and it is possible to prevent ink from soaking into the electrostatic actuators.
(7) A still further aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (2), wherein the diaphragms are formed of a laminated film constituted by a conductive film and a film having a tensile force which is a film-forming stress. It is therefore possible to prevent the diaphragms from sagging. It is possible to prevent the diaphragms from touching the lower layer (individual electrodes) when the sacrificial layer etching is finished.
(8) Another aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (7), wherein the diaphragms are formed by laminating, for example, an Ni layer and a silicon nitride layer on each other. The diaphragms come in contact with the electrodes when the electrostatic actuators are driven. However, there is no fear of abrasion since it is the Ni layer with high hardness that comes in contact with the electrodes. In addition, the silicon nitride layer has enough tension so as not to produce sagging in the diaphragms.
(9) A further aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (2), wherein the diaphragms are formed of a conductive film having a tensile force which is a film-forming stress. It is therefore possible to prevent the diaphragms from sagging even if the diaphragms are of a single layer. It is possible to prevent the diaphragms from touching the lower layer (individual electrodes) when the sacrificial layer etching is finished.
(10) A still further aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (9), wherein the diaphragms are formed by depositing, for example, Pt. Since the diaphragms can be formed of a single layer which is a Pt layer with high hardness and high tension, it is possible to simplify the manufacturing process.
(11) Another aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (2), wherein the sacrificial layer is formed of an organic film, and the sacrificial layer etching is performed by dry etching. By the dry etching, the management of the manufacturing becomes not difficult, unlike wet etching, so that it is possible to simplify the process.
(12) A further aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (2), wherein the independent electrodes are formed on an electrode glass substrate; the independent electrodes are covered with an insulating film; a sacrificial layer is formed on the insulating film; a diaphragm layer is formed on the sacrificial layer; window portions are formed in the diaphragm layer in predetermined positions where support portions of the diaphragms are to be located between the individual electrodes; the sacrificial layer is etched through the window portions to thereby form an electrostatic actuator structure; Ni is subsequently deposited all over the surface and thereafter patterned to thereby form partition base portions to close the window portions; cavity partitions are formed on the partition base portions by Ni electrocasting; and then a nozzle plate is bonded on the cavity partitions. In the present invention, since the sacrificial layer can be formed in a thin film process such as vapor deposition, CVD, or the like, a silicon single-crystal substrate mirror-finished with high precision is not required, and electrostatic actuators can be formed only in such a thin film process. It is therefore possible to use a large-sized glass substrate and thereby improve the productivity. Further, it is possible to obtain a closed structure efficiently, and there is such an advantage that it is possible to prevent ink from soaking into the electrostatic actuators, etc.
(13) A still further aspect of the present invention is an ink-jet recording apparatus equipped with an ink-jet manufactured by any one of the above-mentioned ink-jet head manufacturing methods (2) to (12). Since the ink-jet head manufactured by any one of the ink-jet head manufacturing methods (2) to (12) has no limitation in the material of a substrate, a glass substrate may be used. It is therefore possible to use a large-sized glass substrate, so that it is possible to manufacture a high-performance printer at a low price.
(14) Another aspect of the present invention is an ink-jet recording apparatus equipped with an ink-jet head for a line printer manufactured by any one of the above-mentioned ink-jet head manufacturing methods (2) to (12). Since the ink-jet head manufactured by any one of the ink-jet head manufacturing methods (2) to (12) has no limitation in the material of a substrate, a glass substrate may be used. It is therefore possible to use a large-size glass substrate, so that it is possible to form a multi-nozzle. As a result, it is possible to manufacture a line printer at a low price
(15) A further aspect of the present invention is an ink-jet head comprising a plurality of nozzle holes, ejection chambers independent of each other and communicating with the nozzle holes respectively, electrically conductive diaphragms constituting parts of the respective ejection chambers, and individual electrodes facing the diaphragms through air gaps respectively, and ejecting ink in the ejection chambers toward recording paper through the respective nozzle holes by applying voltages between the diaphragms and the individual electrodes to thereby transform the diaphragms, wherein an insulating film is formed on the individual electrodes.